1. Field of the Invention
The present invention relates to a method of producing an electronic device.
2. Description of Related Art
An electronic device includes a circuit board having electronic parts, and a casing. The casing seals the circuit board except for a connecting terminal to be connected to outside, and is formed by molding thermosetting resin. Specifically, the circuit board is arranged in a cavity of a mold in a float state by using a supporting pin, and the thermosetting resin is filled in the cavity so as to be solidified.
The circuit board has a top face and a back face, and a circuit pattern is typically different between the top face and the back face. For example, positions for mounting the electronic parts are different between the top face and the back face. Therefore, a thickness pattern of the resin molded on the top face may be different from a thickness pattern of the resin molded on the back face, while the resins oppose to each other through the circuit board.
In this case, a hardening speed of the resin may be different between the top face and the back face, due to the difference of the thickness pattern. The difference in the hardening speed of the resin may cause a deformation of the circuit board, because a pressure generated from the resin is different between the top face and the back face. Further, connection reliability of the electronic parts may be lowered, or the electronic parts may have a malfunction, due to the pressure difference.
Further, the supporting pin makes a construction of the mold complicated. Furthermore, the molded casing has a trace of the supporting pin, such that appearance of the electronic device may become worse.
JP-A-2006-303327 discloses a method of producing an electronic device. Electronic parts are mounted on only a first face of a circuit board, and the circuit board is arranged in a cavity of a mold in a manner that a second face of the circuit board opposite from the first face is tightly contact with an inner wall face of the mold. Thermosetting resin is filled in the cavity, and the filled resin is hardened. Thus, a casing of the electronic device is molded by the hardened resin, and the second face of the circuit board defines a part of an outer surface of the electronic device.
In this case, while the casing is molded, only the first face of the circuit board is pressed by the thermosetting resin. Therefore, the circuit board can be restricted from having a deformation, and connection reliability of the electronic parts can be maintained. Further, because the supporting pin is unnecessary, the construction of the mold can be simplified, and the appearance of the electronic device can be made better.
However, a size of the circuit board becomes large, when the electronic parts are mounted on only the single face of the circuit board. In this case, a size of the electronic device also become large.